If svchost was corrupted, I'd expect the entire machine to be unusable considering how many services are required just to start Windows. This does bring up the strong possibility that there is an unrelated problem here that wasn't anything to do with the recent bad McAfee DAT file.

You can try running SFC and reviewing the log file it generates but it sounds more likely that to completely fix the system, you're going to have to do reinstall from scratch.